Make sure that you’ve configured gvim or your terminal emulator to use
a patched font.

You need to set your LANG and LC_* environment variables to
a UTF-8 locale (e.g. LANG=en_US.utf8). Consult your Linux distro’s
documentation for information about setting these variables correctly.

Make sure that vim is compiled with the --with-features=big flag.

If you’re using rxvt-unicode make sure that it’s compiled with the
--enable-unicode3 flag.

If you’re using xterm make sure you have told it to work with unicode. You may
need -u8 command-line argument, uxterm shell wrapper that is usually
shipped with xterm for this or xterm*utf8 property set to 1 or 2
in ~/.Xresources (applied with xrdb). Note that in case uxterm is
used configuration is done via uxterm*… properties and not xterm*….

In any case the only absolute requirement is launching xterm with UTF-8
locale.

If you are using bitmap font make sure that
/etc/fonts/conf.d/70-no-bitmaps.conf does not exist. If it does check
out your distribution documentation to find a proper way to remove it (so that
it won’t reappear after update). E.g. in Gentoo this is:

eselectfontconfigdisable70-no-bitmaps.conf

(currently this only removes the symlink from /etc/fonts/conf.d). Also
check out that no other fontconfig file does not have rejectfont tag that
tells fontconfig to disable bitmap fonts (they are referenced as not
scalable).

If you are using powerline_unicode7top-level theme then symbols for player segments are taken
from U+23F4–U+23FA range which is missing from most fonts. You may fix the issue
by using Symbola font (or any other font
which contains these glyphs).

If your terminal emulator is using fontconfig library then you can create
a fontconfig configuration file with the following contents:

(replace Terminus with the name of the font you are using). Exact sequence
of actions you need to perform is different across distributions, most likely it
will work if you put the above xml into
/etc/fonts/conf.d/99-prefer-symbola.conf. On Gentoo you need to put it
into /etc/fonts/conf.d/99-prefer-symbola.conf and run:

eselectfontconfigenable99-prefer-symbola

.

Warning

This answer is only applicable if you use powerline_unicode7 theme or if
you configured powerline to use the same characters yourself.